This invention relates to injection of pressurized materials through a manifold, such as injection molding of plastic melt in a hot runner system. More specifically, this invention relates to an improved injection molding hot runner system in which the rate of melt flow is controlled through the gate during an injection molding cycle.
U. S. Pat. No. 5,556,582 discloses a multi-gate single cavity system in which the rate of melt flow through the individual gates is controlled independently via a control system according to specific target process conditions. This system enables the weld line of the part (the section of the part in which the melt from one gate meets the melt from another gate) to be selectively located. It also enables the shape of the weld line to be altered to form a stronger bond.
The xe2x80x2582 patent discloses controlling the rate of melt flow with a tapered valve pin at the gate to the mold cavity. It also discloses placing a pressure transducer inside the mold cavity. Placing the pressure transducer inside the mold cavity can result in the pressure transducer sensing pressure spikes which can occur when the valve pin is closed. A pressure spike sensed by the transducer can cause an unintended response from the control system, and result in a less precise control of the melt flow than desired.
The control system disclosed in the xe2x80x2582 patent uses the variables of valve pin position and cavity pressure to determine what position the valve pin should be in. Thus, the algorithm performed by the control system in the xe2x80x2582 patent utilizes two variables to control the rate of melt flow into the cavity.
An injection molding apparatus is provided in which the rate of material flow during the injection cycle is controlled. According to one preferred embodiment, an injection molding apparatus includes a manifold having an inlet for receiving material injected from an injection molding machine, a plurality of injection nozzles coupled to the manifold for distributing the material to a corresponding plurality of gates to one or more mold cavities, and a plurality of sensors respectively associated with each of said plurality of nozzles, each sensor to sense a condition related to the rate of material flow at a location between said inlet and said plurality of gates.